Visualization of protein transport along the secretory pathway using green fluorescent protein

We have expressed green fluorescent protein (GFP) from A. victoria in the secretory pathway of HeLa cells by fusing it to the C-terminus of a secretory protein, chromogranin B. Under normal culture conditions at 37 degrees C maturation of GFP to the fluorescent form was not detectable. However, fluorescent GFP was observed when biosynthetic protein transport was arrested at the intermediate compartment or the trans-Golgi network by temperature blocks (15 degrees C and 20 degrees C, respectively). Reversal of the temperature blocks allowed the visualization of secretion of fluorescent GFP and offers the possibility to analyse transport in the secretory pathway in living cells.